Saturday, December 29, 2012

Top Weather Stories: Derecho

One of the largest severe weather outbreaks to hit the Mid Atlantic in some time was the derecho event that rocked the Mid Atlantic on June 29th into the 30th, an overnight severe event that brought five fatalities to New Jersey during the middle of the night. The setup was a prime one for severe in the Midwest, with a ridge of heat building across the South and Mid Atlantic that pushed high heat into Philadelphia that afternoon as the city reached 98 degrees for a high. Washington hit 104 that afternoon, an "appetizer" to some major league heat that rocked us during the first three weeks of July.

A warm front in the Midwest trailed back to a low center in Iowa that helped spawn thunderstorms early in the morning in the Midwest and also over us, with some severe weather in parts of the Delaware Valley in the pre-dawn hours. The Midwest storms progressed steadily eastward, intensifying as they fed off of a very warm airmass, over the course of the day and earned derecho status as they sustained severe criteria over a long distance and a lengthy amount of time.

The conventional wisdom was that severe weather in the Midwest would fizzle or pass to our south by the time it got this far East. However, the system was able to strengthen and maintain itself across the Great Lakes and Midwest thanks to that high level of heat from that afternoon. Those storms sustained themselves even after sunset, speeding east and southeast across the Appalachians, but also growing on the northern edge of the line as it approached our region.

Power outages in New Jersey lasted upwards of ten days and damage estimates ran in the hundreds of millions across the Garden State. In Delaware, the highest wind gust was nearly 70 mph in Lewes and power was knocked out to tens of thousands at the height of the storm.

In most years, the derecho would definitely make a huge argument for biggest weather story for the region overall. This year arguably wasn't one of those.